The telephone is a boon to mankind. It provides communications over short or long distances to call emergency assistance, conduct business negotiations or simply to pass the time of day between friends. Without this aid, civilization as we know it would not be possible. However, with the advent of more sophisticated telephone systems such as automatic dialing and computer operated voice and response systems, unscrupulous entrepreneurs have turned the telephone from a friendly device into a demon capable of harassing anyone with a telephone with unsolicited sales promotions, messages and the like.
When a salesman rings your door bell you don't have to answer. But with a telephone, when it rings you have to pick it up to find out who is there. If it's an unsolicited call relating to a sales promotion or other form of harassment, many times the answering party is trapped into listening to the message. This practice of unsolicited telephone calls for sales and advertising purposes has become such an annoying burden that many people have installed telephone answering machines which require a calling party to leave a message. Then the person using the answering machine plays back a tape or listens to the incoming message in real time and makes a decision to answer the call or return the call. This is costly and time consuming and the individual is still bothered by the unsolicited calls because a certain amount of time has to be devoted to listen to the message to identify just what type of call it is.
Numerous attempts have been made to provide a security device which is inexpensive and convenient for the user but these devices have numerous shortcomings. For instance, J. Smith in U.S. Pat. No. 4,520,233 on "Telephone Line Security Apparatus" issued May 28, 1985 discloses a device which is placed at a subscriber's station to intercept incoming calls. The intercepted calls are monitored for a coded message and if a proper code is transmitted, the line is terminated and an automatic call back is made to the calling number associated with the code to provide added security. This system is extremely elaborate and requires added expense for the user, especially if long distance telephone calls are involved because the calling party merely has to initiate the call and then the receiving party has to pay the greater charges for initiating a second call plus the time charges during the course of the following conversation.
M. Castro et al, U.S. Pat. No. 4,369,339 on "Method For Completing The Connection Between A Telephone Exchange And The Phone Subscriber's Line In Response To The Reception, At The Exchange, Of A Pre-Established Code" issued Jan. 19, 1983 describes a system which requires the calling station to transmit a proper code before the call is completed to the subscriber's handset. In this system the decoding operation occurs at the last distribution point of the network prior to the subscriber's line. Therefor, the subscriber has no control over the system and in reality it is a piece of network equipment.
P. Giorgio et al, U.S. Pat. No. 4,611,098 on "Coded Telephone Access System" issued Sep. 9, 1986 discloses a subcriber station security device which automatically answers a telephone call, checks the incoming call for a proper coded signal and if the coded signal is received, it completes the call. If a coded signal is not received within a predetermined time period, the call is automatically terminated. In this system an overly complex and expensive circuit design is utilized. This complex system has resulted in a product which is costly to manufacture and maintain and not user friendly. It uses excessive current, will not go to an "on-hook" condition after a predetermined, will not wait a predetermined number of rings before going into the answer mode, and will not automatically reset when the phone line transitions from "off-hook" to "on-hook". Therefor, it has not met with economical success even in view of the grave need for such an apparatus.